Fix stop sequence check to handle empty strings correctly

Author: chahn

src/smolagents/models.py

@@ -84,7 +84,7 @@ def remove_content_after_stop_sequences(content: str | None, stop_sequences: lis
         return content
 
     for stop_seq in stop_sequences:
-        if not stop_seq:
+        if stop_seq == "":
             continue
         split = content.split(stop_seq)
         content = split[0]